1. Field of the Invention
The present invention is generally related to a nuclear steam supply system (NSSS) resistance temperature detector (RTD) nozzle mechanical clamp seal assembly and blowout retainer designed to prevent leakage from or around an RTD nozzle and blowout of the nozzle from its joint or seat in NSSS piping.
2. General Background
The resistance temperature detectors measure the nuclear reactor coolant temperature in both the "hot" and "cold" legs of the NSSS. The RTD's are installed through the welded penetrations in the Reactor Coolant System (RCS) piping. The penetrations are susceptible to cracking and leakage caused by primary water stress corrosion cracking (PWSCC) of the, typically, Inconel 600 stainless steel nozzles. The present repair method for these nozzles requires a lengthy and expensive welding procedure which increases the amount of work and time required to restore the NSSS to operation once this type of cracking and deterioration occurs.
Examples of this type of technique in repairing pressurized heater sleeve penetration nozzles which involve analogous pressure boundary welding procedures are disclosed in U.S. Pat. No. 5,094,801 dated Mar. 10, 1992 by Dixon et al., U.S. Pat. No. 5,091,140 dated Feb. 25, 1992 by Dixon et al., and U.S. Pat. No. 4,255,840 dated Mar. 17, 1991 by Cook et al.
The RTD nozzle mechanical clamp seal of the invention prevents reactor coolant leakage at the RTD nozzles without the necessity of such a welding procedure.
In U.S. Pat. No. 4,655,483, filed May 14, 1984, entitled "Boundary Seal for Pressure Penetration", and assigned to the assignee of the present invention, a connector device provides a primary pressure boundary between a nozzle and a column concentrically disposed therein. The connector device includes a closure member for compressing a seal ring against the end of a nozzle. The closure member includes a hub portion which defines an annular space between the closure member and the column. Packings are inserted in this annular space and compressed by means of a drive unit which includes a drive sleeve and an actuator nut threaded to an upper portion of the sleeve. A split-ring type collar is clamped to the column to provide support for the column. Rotation of the actuator nut loads the column thus causing it to be longitudinally displaced relative to the closure member until a tight connection is made. Continued actuation of the nut advances the drive sleeve along the annular space to compress the gasket to thereby complete the fluid-tight connection. While the boundary seal of the referenced prior art application can be installed in a relatively short time when compared to previous devices of like character, it nevertheless requires substantial effort to install the connector, particularly the collar clamp which has eight bolts to tighten. Further, this boundary seal assembly does not completely insure against the column assembly accidentally moving upwardly or downwardly during the assembly process.
In U.S. Pat. No. 4,723,795 filed May 5, 1996, entitled "Instrument Penetration For High Pressure Vessels", and assigned to the assignees of the present invention, an assembly provides a fluid-tight connection between a nozzle and a concentric tubular column supported in the nozzle. The nozzle is provided with an interior flange while a ledge extends from the exterior of the column at a point which will be displaced from the nozzle flange when the column is disposed in the nozzle. A seal assembly, which comprises an annular packing or sealing ring, is positioned on the flange and surrounds the column for establishing a seal between the nozzle and the column. A drive sleeve is received within the nozzle. The drive sleeve has a first end, which bears against the seal assembly, and a drive shoulder. A spacer sleeve is threadedly received in the nozzle for axial positioning relative thereto. A first end of the spacer sleeve is configured for engagement with the column ledge. A clamp assembly is mounted to the column at a fixed axial position relative to a first end of the nozzle. The clamp assembly includes an adjustable means for axially displacing the column relative to the nozzle so that the column ledge firmly engages the lower end of the spacer sleeve to fix the axial position of the column relative to the nozzle. A drive means, which comprises a nut threaded to the nozzle, is engageable with the drive shoulder of the drive sleeve to axially force the drive sleeve first end toward the nozzle flange to compress the sealing assembly into sealing engagement with the column and the nozzle to prevent fluid leakage therebetween. This prior art assembly provides a fluid-tight connection between a nozzle, which has an interior flange, and a column, which is concentrically supported within the nozzle
Further background and prior art information is provided by a paper "Repair Method for Control Rod Drive Stub Tube Using a Mechanical Graphite Seal" by C. W. Ruoss, Jr. et al, presented at the EPRI and EPRI NDE Center Sponsored BWR Reactor Pressure Vessel & Internals Inspection & Repair Workshop, Jul. 16-18, 1991, Charlotte, N.C.